We had a pleasant night camping in the Mammoth Cave National Park campground, then got up for an excursion in the caves. Mammoth Cave National Park is the home of the longest known cave sysyem in the world, traversing 390 miles underground. We had made reservations the night before for the “Grand Avenue Tour.”

The tour was a ranger-led, 4 1/2 hour, 4 mile underground hike in the cave. It started by descending from ground level, going down stairs in a man-made tunnel, about 200 feet below the surface. At the deepest point, we were 290 feet below the surface.

Once at the bottom, our ranger gave us a little cave geology lesson, explaining that the caves were formed millions of years ago by surface water eroding the limestone that lies beneath the sandstone cap rock through two processes, physical friction and chemical reaction – the water and the calcium create an acid that further dissolves the limestone.

This process creates tunnels that water flowed through many years ago.

Along the walls of these underground tunnels, a salt-like rock called gypsum forms. It is used in drywall and also as an additive to beer! It forms beautiful shapes. We wanted to take a sample for our favorite rock collector, Dorothea, but it wasn’t allowed.

Something else we saw on the tunnel walls was 150 year old graffiti, like this one from 1863 by a Civil War soldier, Wad Wallace. It was made with soot from a candle.

It was really dark down in the cave and my camera doesn’t take very good flash photos, but here’s what it looked like as we walked along the underground trail. In places, we walked through slot canyons like those we saw above ground in Arizona.

At one point, they turned out the lights and told us to all be quiet. Now I know what it would feel like to be blind and deaf. Here’s what it looks like with the lights out down there. 😉

At the end of the 4 miles, we came to the area where stalactites and stalagmites had formed. It was very pretty, but for this kind of thing there’s no comparison to Carlsbad Caverns in New Mexico.

They called this one “Niagara Falls.”

It was a relatively short hike up to exit because the surface, being hilly, had sloped down to our elevation,

Tonight, we’re back urban camping at Walmart in Bowling Green, Kentucky, about to go root for the Cardinals in game 5 of the World Series. Go, Cards!